a) Field of the Invention
This invention relates to a color display device and more particularly to a color display device comprising a multiplicity of display areas.
b) Description of the Related Art
A flat panel such as a liquid crystal display (LCD), a plasma display panel (PDP) and the like is widely used as a display device.
Recently, color LCDs and color PDPs that have a variety of abilities in color display are commonly used Usually color filters are used to perform color display while utilizing the advantages of a flat panel, such as thinness, lightweight and the like.
A color filter is a filter that transmits only such visible light that has a selected wavelength range. Corresponding to the principles of light mixing and separating, there are three-primary-color filters, which are red (R), green (G) and blue (B) filters, and complementary-color filters, which are cyan (C), magenta (M) and yellow (Y) filters.
A color display device for performing optional color display comprises a multiplicity of unit display regions on which predetermined color filters are disposed. The color display device performs desired color display by controlling transmission or reflection of each unit display. In order to make a display image vivid by preventing color mixing, it is widely performed that an area of each unit display region is demarcated by covering the periphery thereof with a black matrix (BM) such as metal, opaque resin and the like. In that case, an opening of the BM will be the unit display region that will be also a light transmissive region.
A liquid crystal display (LCD) will be described hereinbelow, as an example of the color display. An LCD controls an optical characteristic of a liquid crystal layer sandwiched between a pair of substrates with respective electrodes by impressing voltage across the liquid crystal layer. Transmissivity of light as a whole is controlled, if necessary, by combining a polarizer or polarizers. A pair of transparent substrates such as glass or the like is used for a transmissive-type display device. For a reflective-type display device, at least one of two substrates through which light transmits is a transparent substrate.
There are known systems for driving a display region; one is the simple matrix system in which a plurality of electrodes (common electrodes and segment electrodes) crossing each other are formed on a pair of facing substrates, and another is the active matrix system in which a whole surface electrode (a common electrode) is formed on one substrate, and a picture-element (pixel) electrode and a switching transistor are formed in each unit display region on the other substrate in order to store desired voltage in each pixel.
To realize the active matrix display with glass substrates, a thin film transistor (TFT) made of amorphous silicon (a-Si) or polycrystallized silicon (poly-Si) is used as material for forming a switching transistor. One current electrode (hereinafter, referred to as a source electrode) of TFT is connected to a pixel electrode, and the other (hereinafter, referred to as a drain electrode) is connected to a data line. A control electrode (a gate electrode) is connected to a scanning line, and the data and the scanning lines are configured to cross each other on the substrate.
It is preferable for a color display to have high color reproducibility and a high transmissivity of light. The color reproducibility depends on the coordinates of chromaticity. In case of RGB-type, a wider area of a triangle formed on the coordinates of chromaticity with each of color filters (red, green and blue) makes higher color reproducibility. The transmissivity of light depends on the output-light intensity when white light is irradiated on each color filter and on an aperture ratio of the BM.
A high transmissivity of light is desired to get a bright color display, especially in a color LCD for a notebook computer and in a reflective-type LCD. In such a case, it is desired to increase the aperture ratio of the BM by narrowing a width of the BM between the light transmissive regions, and to increase the transmissivity of color filters by thinning the color filters or changing their material.
The color filters cover a whole surface of each light transmissive region, which is referred to as the unit display region, and are configured to overlap the BM surrounding the light transmissive regions. Narrowing the width of the BM might risk adjacent color filters overlap each other, which may cause aberrant thickness and lower a yield of the production process. It requires new experiments to determine new conditions to change a film thickness of color filters or material for changing a design of an LCD, and causes lowering in throughput and productivity in a mass production.